The present invention relates generally to pneumatic fastener driving tools, and more particularly to a new and improved pneumatic fastener driving tool wherein the tool has incorporated therein a control system which ensures the safe operation of the tool while effectively permitting the operation of the tool within either one of two rapid fire modes.
Pneumatic fastener driving tools are well known in the art and are exemplified by means of U.S. Pat. No. 4,550,643 which issued to Schwartzenberger on Nov. 5, 1985, U.S. Pat. No. 4,405,071 which issued to Austin on Sep. 20, 1983, and U.S. Pat. No. 3,888,404 which issued to Ramspeck et al. on Jun. 10, 1975. Such fastener driving tools conventionally incorporate therein trigger and workpiece contact mechanisms both of which must be activated in order to achieve the discharge or firing of a fastener from the tool. More particularly, a mechanical linkage is operatively connected to a pilot valve such that activation of the pilot valve by means of the mechanical linkage causes the fastener driving tool to cycle and thereby discharge or fire a fastener. The linkage is constructed in such a manner that the movement required to activate the pilot valve is derived from the combined movements of the trigger and workpiece contact mechanisms, although the trigger and workpiece contact mechanisms do not have to be depressed or actuated in any particular manner or order.
Accordingly, if, for example, an operator manipulates or holds the tool in such a manner that the workpiece contact element or mechanism of the tool is constantly maintained in contact with the workpiece or structure, then the tool can discharge or fire a fastener whenever the trigger element or mechanism is also depressed. This mode of operation of the tool is commonly known or referred to as xe2x80x9ctrigger firingxe2x80x9d and obviously provides the operator with a first mode of operation or means for achieving a high level of productivity. This mode of operation is also appreciated to be inherently safe because the workpiece contact element or mechanism is always disposed in contact with a workpiece prior to depression or actuation of the trigger element or mechanism. Alternatively, if, for example, the operator grasps the fastener driving tool by means of its handle in such a manner that the trigger element is constantly depressed, then the tool can discharge or fire a fastener whenever the workpiece contact element is also depressed. This mode of operation of the tool is commonly known or referred to as xe2x80x9cbump-firingxe2x80x9d and provides the operator with a second mode of operation or means for achieving a high level of productivity. The obvious disadvantage of this mode of operation of the tool is that the tool can be accidentally, inadvertently, or unintentionally discharged or fired if, for example, while the operator is carrying or transporting the tool between different worksites, and while the trigger element is depressed, the workpiece contact element of the tool is inadvertently, accidentally, or unintentionally depressed such as, for example, when the workpiece contact element is accidentally, inadvertently, or unintentionally engaged or moved into contact against some relatively solid object, including the operator, another person, or onsite worker, other than an intended workpiece.
Accordingly, safer versions of pneumatic fastener driving tools require that the trigger and workpiece contact elements of the tool be depressed in a particular order in order to discharge or fire the tool, that is, the workpiece contact element must first be depressed against an intended workpiece, and subsequently, the trigger element must then be actuated. This mode of operation of the fastener driving tool is commonly known or referred to as xe2x80x9csequential firingxe2x80x9d. Mechanical linkages incorporated within such tools therefore require that the trigger mechanism must be released and subsequently again depressed or actuated each time a fastener is to be discharged or fired. While the operation of this type of fastener driving tool is thus rendered safer than the previously noted xe2x80x9cbump-firexe2x80x9d type of fastener driving tool, it can be readily appreciated that this type of fastener driving tool does not permit the tool operator to achieve a level of productivity which is comparable to that achieved by means of the aforenoted type of fastener driving tool which is being operated in the xe2x80x9cbump-firingxe2x80x9d mode.
Accordingly, a need exists in the art for a new and improved pneumatic fastener driving tool wherein the trigger and workpiece contact elements are not required to be depressed or actuated in a particular manner or order whereby the tool is able to be operated in both high-speed bump-fire and trigger-fire modes of operation, and yet, the tool is also able to be operated in a safe manner so as to prevent the inadvertent, accidental, or unintentional discharge or firing of the tool despite the fact that an operator may carry or transport the tool between different worksites with the trigger element constantly depressed.
Accordingly, it is an object of the present invention to provide a new and improved pneumatic fastener driving tool.
Another object of the present invention is to provide a new and improved pneumatic fastener driving tool which effectively overcomes the various disadvantages and operational drawbacks characteristic of PRIOR ART pneumatic fastener driving tools.
An additional object of the present invention is to provide a new and improved pneumatic fastener driving tool which is able to be operated in either one of two high-speed bump-fire and trigger-fire operational modes.
A further object of the present invention is to provide a new and improved pneumatic fastener driving tool which is in effect a hybrid type pneumatic fastener driving tool in that the tool is able to be operated in either one of two high-speed bump-fire and trigger-fire operational modes and yet, under certain circumstances, in order to render the tool safe during periods in which fasteners are not to be discharged or fired, the tool cannot be recycled or again discharged or fired unless the tool is initially activated in accordance with a sequential firing mode of operation subsequent to which the tool can also again be discharged or fired in either one of the two high-speed bump-fire or trigger-fire operational modes so as to achieve the desirable high level of productivity.
The foregoing and other objectives are achieved in accordance with the teachings and principles of the present invention through the provision of a new and improved pneumatic fastener driving tool which comprises a housing within which a main valve is disposed and which is adapted to be vented through means of a pilot valve assembly. A workpiece contact element linkage mechanism is operatively connected to a fill valve which is movable so as to fluidically connect the interior of the tool handle, into which compressed air is conducted by means of a suitable fitting, to a reservoir tank. The reservoir tank is in turn fluidically connected to an enable valve assembly so as to provide signal air thereto, and a trigger element or mechanism is operatively connected to the pilot valve assembly as well as to a relief valve assembly.
Accordingly, and initially, when the workpiece contacting element is engaged with a workpiece prior to the depression of the tool trigger element or mechanism, the compressed air is permitted to enter the reservoir tank through means of the fill valve so as to provide the reservoir tank with pressurized reservoir air, the pressurized reservoir air maintains the relief valve assembly closed and is also conducted to the enable valve assembly by means of a signal line, and the compressed air also pressurizes the main valve through means of the pilot valve assembly and the enable valve assembly. Upon subsequent depression of the trigger element or mechanism, the pilot valve assembly is opened, the pressurized reservoir air maintains the relief valve assembly closed against the biasing force of the trigger element or mechanism, and the air signal from the reservoir tank to the enable valve assembly maintains the enable valve assembly opened such that the main valve is able to be vented through means of the enable valve assembly and the pilot valve assembly whereby a fastener is able to be fired or discharged. If the trigger element or mechanism is depressed prior to the engagement of the workpiece contacting element with a workpiece, the reservoir tank is not sufficiently pressurized, the pressure level within the reservoir tank is therefore insufficient to maintain the relief valve assembly closed or to actuate the enable valve assembly, the relief valve assembly is thus opened, and when the workpiece contacting element is subsequently engaged with the workpiece and thereby also opens the fill valve, the compressed air is immediately vented through the relief valve assembly whereby the tool will not fire or discharge. Consequently, in order to initially activate or operate the tool, the tool must be operated in a sequential firing mode comprising the engagement of the workpiece contacting element or mechanism with a workpiece prior to the actuation or depression of the trigger element or mechanism. Subsequent to such an initial activation or operation of the tool, additional operational cycles of the tool, wherein additional fasteners are able to be fired or discharged, can in fact be achieved regardless of whether or not the trigger element or mechanism is depressed prior to the contact or engagement of the workpiece contacting element or mechanism with a workpiece. This is because sufficient pressurized air is already contained and retained within the reservoir tank, such pressurized reservoir air maintains the relief valve assembly closed and is able to supply signal air to the enable valve assembly, and in addition, such pressurized reservoir air is additionally replenished or supplemented through the fill valve every time the workpiece contacting element or mechanism is engaged with a workpiece whereby the fill valve is actuated.
In this manner, the rapid fire modes of operation, comprising either the xe2x80x9cbump-firingxe2x80x9d or xe2x80x9ctrigger-firingxe2x80x9d modes of operation, can be achieved. As has been noted hereinbefore, the xe2x80x9ctrigger-firingxe2x80x9d mode of operation of the tool is inherently safe because each time the trigger element or mechanism is depressed so as to fire or discharge the tool, the workpiece contact element or mechanism is already disposed in contact with the workpiece. In order to render the tool safe, however, when the tool is being operated in the xe2x80x9cbump-firingxe2x80x9d mode, whereby the inadvertent, accidental, or unintentional firing or discharge of the tool is to be effectively prevented, a bleed orifice is fluidically connected to the reservoir tank whereby the pressurized reservoir air is constantly but slowly bled from the reservoir tank. Therefore, in order for the tool to be fired or discharged, sufficient pressurized air must be maintained within the reservoir tank so as to maintain the relief valve assembly closed and to provide the necessary signal air to the enable valve assembly when the workpiece contact element or mechanism is subsequently depressed such that the workpiece contact element or mechanism, along with the trigger element or mechanism which is already depressed, activates the pilot valve assembly. Sufficient pressurized air is only maintained within the reservoir tank by means of the actuation of the fill valve as a result of the actuation or depression of the workpiece contact element or mechanism against a workpiece.
Therefore, if the workpiece contact element or mechanism is again depressed against or disposed in contact or engagement with a workpiece within a predetermined period of time after its previous contact or engagement with a workpiece, sufficient pressurized air will again be introduced into the reservoir tank, or in other words, the pressurized air within the reservoir tank will have been replenished. However, if the workpiece contacting element or mechanism is not depressed or disposed in contact with a workpiece within a predetermined amount of time after its previous contact or engagement with a workpiece, whereby the pressurized air present within the reservoir tank has already been bled to a predetermined degree and has not therefore been sufficiently replenished or supplemented by new pressurized air attendant the engagement or contact of the workpiece contacting element or mechanism with a workpiece and the resulting operation of the fill valve, insufficient air pressure is thus retained or present within the reservoir tank, and therefore the relief valve will be opened, the pressurized air within the reservoir tank will be vented, the enable valve will be closed, and the operative firing or discharge cycle of the tool will be rendered inoperative when the tool is to be fired or discharged by means of the depression of the workpiece contact element or mechanism against a workpiece because the pressurized air now introduced into thereservoir tank by means of the fill valve will now be immediately vented through the relief valve assembly. This mode of operation thus renders the tool safe to transport between job sites or work sites despite the fact that the operator may carry or transport the tool by means of the handle with the trigger element or mechanism constantly depressed.